Hoop stent

ABSTRACT

A wire frame stent and stent delivery system for inserting the stent into the body.

FIELD OF THE INVENTION

This invention relates to stents for use in vascular surgery.

BACKGROUND OF THE INVENTION

A wide variety of stent designs have been proposed for use in thevascular system. Typically, the stents are used to hold open a length ofblood vessel which has been closed or occluded by some growth within theblood vessel. Balloon expandable stents and self-expanding stents arecommercially available and have been used successfully for treatment ofa number vascular diseases. Das, Stent, U.S. Pat. No. 5,554,181 (Sep.10, 1996) shows a wire stent having a number of hoops all attached to aradially disposed spine, all of which may be formed of a single wire.Likewise, Hillstead, Endovascular Stent Apparatus and Method, U.S. Pat.No. 4,856,516 (Aug. 15, 1989). The stents are folded upon a catheterpusher and retained within a catheter sheath before release into thebody. These stents must be radially compressed to fit within thecatheter sheath, and expand elastically or may be expanded inelasticallyby a balloon. They are not susceptible to being stretched or elongatedin the along their long axes to reduce their overall diameter.

SUMMARY

The stent and stent delivery system described herein are designed forinsertion into blood vessels and other lumens of the body. Theself-expandable stent is composed of a single small diameter (0.005inch) nitinol wire which is doubled first by making a bend at itsmid-portion. The wire pair is then led around a tubular jig to form ahoop, and the wires are joined by double twisting or point welding toform a strut, then led around the tubular jig to form another hoop,joined to form another strut, and so on until the desired number ofhoops are formed. The stent may be stretched along the long axis of thestent, whereupon the hoops are deformed into ellipses disposed at anangle approximately midway between the long axis of the stent and theradius of the stent, and the overall diameter of the stent is reduced bythis deformation.

To deploy the stent, it is stretched out completely on the surface of asmall catheter (3-F). The catheter contains a specially designed angledtip guide wire provided with a low-profile hook. The front end of theconstrained stent is hung on the hook. The hook comes out from thecatheter's lumen through a hole and goes back into the catheter throughanother hole. A monofilament retrieving loop runs from the proximal endof the deployment catheter to the to the proximal end of the stent. Theproximal end of the retrieving loop is fastened to a sliding ringattached to the proximal end of the 3-F catheter shaft. Before finalrelease of the stent, the retrieving loop may be operated via thesliding ring to pull the stent in order to correct for any error in theinitial placement of the stent. After the stent is properly placed andthe retrieving loop may be severed to release the stent from thedelivery catheter. The stent has thermal shape memory orpseudoelasticity which facilitates deployment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the stent.

FIG. 2 is a view of the stent in a stretched condition for loading ontothe delivery catheter.

FIG. 3 is a cross-section of the delivery catheter for use with thestent.

FIG. 4 is a view of the delivery catheter for use with the stent.

FIG. 5 is a radial cross-section of the delivery catheter for use withthe stent.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the stent in its expanded state. The stent 1 is comprisedof a single wire 2 which is folded at a point along the wire, such asmid-point 3 to form a length of double wire comprising two wiresegments. Several twisted sections 4 in the double wire are interspersedwith several hoops 5 formed by pulling the double wire apart into thehoop shape. The double wire is then bent at each junction 6 between thetwisted sections and the hoops to form an angle of about 90° betweeneach hoop and twisted section. The twisted sections 4 create alternatelyradially opposed struts or spines 7 between successive hoops. The freeends 8 of the wire 2 may be twisted into a free spine as shown, or theymay be joined together. The hoops in this arrangement are aligned alonga common axis 9 which defines the longitudinal axis of the stent, andthey are oriented approximately parallel to each other. The stent has anunconstrained diameter defined by hoop diameter 10. The hoops may be allthe same overall diameter, or they may be of different diameter, and itmay be particularly useful to create the hoops so that the size of thehoops increases from one end of the stent to the other. The struts maybe all the same length or of varying length. Although shown as beingformed by intertwining the tow wire segments, the struts maybe formed bywelding the segments together, or by shaping the segments to runparallel where the strength of the wire permits. Note that the stent maybe formed of two separate lengths of wire, but in this case a free endstrut at distal hoop 5d, or a joint provided elsewhere along the stent,may be required.

FIG. 2 shows the stent stretched out in the condition that it will beloaded onto the delivery catheter. In its stretched condition, the hoops5 have elongated into reclining ellipses 11 oriented at an angle fromthe longitudinal axis 9 of the stent 1. The angle is intermediatebetween the longitudinal axis of the stent and the radius 12 of thestent. Thus the overall diameter of the stent has been significantlyreduced by stretching along the longitudinal axis. The fact that thestruts are not radially aligned permits longitudinal stretching ordeformation of every hoop in the stent. As illustrated, the each strutis radially opposed to the struts on either side, meaning the each strutis on the opposite side of the stent compared to the preceding orsucceeding strut. When the adjacent struts are 180° apart, maximumstretching of the hoops is achieved merely be pulling the ends of thestent. Direct opposition, or opposition of exactly 180°, is not requiredto obtain the benefit of this construction, and it suffices that thestruts not be radially aligned.

The stent wires 2 may be made of a shape memory alloy such as nitinol(or other shape memory material), pseudoelastic or superelastic alloysuch as nitinol (or other pseudoelastic or superelastic material),spring metal such as stainless steel, or other suitable materials. Whenmade of shape memory nitinol or superelastic nitinol, the stent may betrained to the shape shown in FIG. 1, and will revert to that shapeeither through shape memory behavior at its chosen transitiontemperature, or through superelastic behavior at body temperature. Theappropriate compositions and training regimens may be used to obtainthese characteristics. Spring materials such as stainless steel may beused also, and fabricated so that the shape of FIG. 1 is the relaxedstate of the material which is regained elastically after stretchinginto the shape shown in FIG. 2. As with prior art stents, the stent mayalso be deployed by inflating a balloon within the stent.

FIG. 3 shows a cross-section of the delivery catheter for use with thehoop stent shown in FIGS. 1 and 2. The delivery catheter 13 is amulti-lumen catheter, preferably with at least two lumens, a guide wirelumen 14 and a retaining loop lumen 15. A guide wire 16 is disposedwithin the guide wire lumen 14 and a retaining loop 17 is disposedwithin the retaining loop lumen 15. The guide wire 16 may be anyavailable guidewire, such as an 0.012 coronary guidewire, and may havean angled or curved soft tip 18 as shown. The retaining loop 17 may beany small diameter wire or thread, made of metal, suture, nylon or othersuitable material. The delivery catheter 13 may be made of polyethylene,polyester or any other suitable catheter material, and may be made inconvenient length (about 100-135 cm for coronary applications) anddiameter (about 3 French (1 mm) for coronary applications).

The guide wire 16 is modified by the addition of a retaining hook 19attached several centimeters proximal to the distal end of theguidewire, at a location corresponding to the distal end of both thedelivery catheter 13 and the stent 1. As shown in FIG. 3, the deliverycatheter has two retaining hook apertures 20d and 20p. The retaininghook exits the proximal aperture 20p and re-enters the catheter throughthe distal aperture 20d, and the external portion 21 of the hook traps asection of the stent 1 between the retaining hook and the deliverycatheter.

The retaining loop 17 is threaded through the pair of apertures 22p and22d. The retaining loop 17 enters the retaining loop lumen through theproximal aperture 22p, and exits the lumen through the distal aperture22d, where it loops around a portion of the wire 2 at the distal end ofthe stent. The proximal end 23 of the retaining loop is secured to asliding ring 24 slidably mounted on the delivery catheter proximal end.FIG. 5 shows a radial cross-section of the delivery catheter alongsection a of FIGS. 3 and 4, with the guidewire 16 inside the guide wirelumen 14 and the retaining loop 17 within the retaining loop lumen 13.

The position of the stent 1 on the delivery catheter 13 is illustratedin FIGS. 3 and 4. The stent is stretched in order to flatten the hoops.A distal hoop 5d is retained by the retaining hook 19, while a proximalhoop 5p is retained by the retaining loop 17. Because the stent isstretched between the retaining g loop and the retaining hook, the hoops5 and spines 7 are pulled taught against the delivery catheter, and theouter diameter of the entire assembly is reduced in comparison to theouter diameter of the expanded stent.

In use, a guiding catheter is used to catheterize the main trunk of thecoronary artery (or other blood vessel to be stented). The guidingcatheter is inserted percutaneously into the femoral artery and pushedinto place near the coronary artery to be stented. The deliverycatheter, preferably a 3 F double channel catheter with the completelystretched stent, is advanced into the lumen of the guiding catheter. Thecatheter-stent unit is advanced into the vessel so that the leading endof the stent can be in the right position. As a first step, the slidingring is unlocked and moved slowly distally allowing the stent to take onits unconstrained diameter. Using the sliding ring carefully and takingadvantage of the thermal memory of the stent, a smooth and controlleddeployment can be achieved. At this point, some contrast can be injectedvia the side port of a check-flow adapter (not shown) which is attachedto the guiding catheter. If the deployment is considered unsatisfactory,the retaining loop offers the chance of reposition. By pulling thesliding ring back (proximally) on the catheter, the stent can bestretched completely again. The delivery catheter's position can bechanged with manipulation through the retaining loop 17, and the stentcan be deployed again. When the deployment is completed, one of thestrands of the retaining loop 17 is cut and the retaining loop 17 ispulled out. (Thus the retaining loop serves also as a release/retrievalloop. Note that the retaining loop 17 may be beneficially used withouttaking advantage of the retrieval function.) Following this maneuver,the guide wire 16 is pulled proximally within the delivery catheter tounhook the stent from the retaining hook. The guide catheter and thedelivery catheter 13 are removed together completely.

While the preferred embodiments of the devices and methods have beendescribed in reference to the environment in which they were developed,they are merely illustrative of the principles of the inventions. Otherembodiments and configurations may be devised without departing from thespirit of the inventions and the scope of the appended claims.

We claim:
 1. A device comprising:a stent comprising a plurality of hoopsconnected by struts; said stent being mounted upon an insertion cathetertube having at least one lumen within the tube, said insertion cathetertube having at at least one retaining clip side aperture near a distalend of the stent and at least one retaining loop side aperture near aproximal end of the stent; a retaining loop extending from the proximalend of the insertion catheter tube, through a lumen in the insertioncatheter tube and out the retaining loop side aperture and engaging thestent to secure said stent to the insertion catheter tube; a retainingclip extending from a lumen in the insertion catheter tube and out theretaining clip side aperture and engaging the stent to secure it to theinsertion catheter tube; said retaining clip being operably connected toa wire in the lumen of the insertion catheter tube, where said wireextends to the proximal end of the insertion catheter and is operable towithdraw the retaining clip from engagement with the stent; saidretaining loop being severable to release the stent from retention bythe retaining loop.
 2. The device of claim 1, wherein:the stent ischaracterized by an unconstrained diameter and a longitudinallystretched diameter, and the stretched diameter is smaller than theunconstrained diameter, and the stent is mounted on the insertioncatheter tube in the stretched condition having the smaller stretcheddiameter and secured to the insertion catheter tube by the retainingloop and retaining clip; and the stent may be released from theinsertion catheter tube by withdrawing the retaining clip fromengagement with the stent and severing the retaining loop to release thestent from retention by the retaining loop, whereupon the stent mayexpand to its unconstrained diameter.
 3. The stent of claim 1, whereinthe stent is comprised of a shape memory material.
 4. The stent of claim1, wherein the stent is comprised of a pseudoelastic material.
 5. Thestent of claim 1, wherein the stent is comprised of a shape memorynitinol.
 6. The stent of claim 1, wherein the stent is comprised of apseudoelastic nitinol.